Four projects, each involving various aspects of lung function measurement, are included in this application. (1) Most data concerning the properties and function of the lung lining layer have been inferred from in vitro studies. A series of investigations from this laboratory over the past six years based directly on pressure-volume measurements of excised and intact lungs have suggested that important differences between intact lining and in vitro lining probably exist. This project aims to continue the study of in situ properties of the alveolar lining, at the same time to elucidate the interpretation of certain features of pressure-volume curves and of gas trapping. (2) A primate model of IRDS has been developed, and a collaborative study of the functional, structural and biochemical development of these premature monkey lungs has begun. Lung mechanical data obtained through this project will be correlated with other types of data obtained by collaborators in Pediatrics. Emphasis is placed on delineating the natural history of HMD during the first hours and days of life, and of documenting the efficacy of prenatal or postnatal therapy. (3) A second collaborative study is underway in which experimental interstitial lung disease is produced in rabbits. Immunologic pharmacologic and histopathologic studies are performed by others while physiologic criteria of lung injury are established by this project. Acute and chronic inflammation are induced by Con A and/or BSA aerosol inhalation. (4) Several hypotheses exist concerning the mechanical origin of cardiogenic oscillations in the exhaled N2 concentration during the single-breath O2 test. Experiments are designed to determine the separate contributions to these oscillations in dogs from ventricular wall motion, large parahilar vessel pulsations, and small alveolar vessel pulsations. Their regional origins will be localized by bolus injections of N2 via catheters in various lung segments and lobes.